The present invention is generally related to motor controllers, and more particularly to an open-loop speed controller integrated circuit ("IC") for alternating current ("AC") induction motors.
One advantage of induction motors as compared to permanent magnet synchronous motors is the ability to change air gap flux. This allows greater than base speed operation by reducing the flux to operate in a constant power region. However, motor current must be adjusted to match motor load in order to achieve efficient operation.
One known technique for matching motor current to motor load is vector control. Vector control employs secondary flux rotational speed and a torque command signal to control stator current frequency and amplitude. However, vector control requires a speed sensor to be placed near to the motor in order to sense motor rotation frequency, and such a speed sensor increases controller cost and may be more susceptible to electromagnetic interference.
U.S. Pat. No. 4,967,135 issued to Ashikaga et al describes a sensorless induction motor vector controller in which a vector controlled flux calculator is employed to estimate rotor speed from motor phase currents and d and q axis flux and torque commands. The sensorless controller estimates the rotor speed by other than measurement means. However, this controller is relatively complicated to implement and may be costly to produce.